AUTOCLAVE VALIDATION – WHAT IS REALLY REQUIRED?
PO Box 10907 Vorna Valley 1686
Steam autoclaves have been with us for many
years and are used in many different industries.
Their primary task is to sterilize items so that
these same items can be used in situations
where the introduction of micro-organisms
would pose a health-risk. But how can we be
sure that the autoclave is doing its job?
Biological indicators form part of this validation,
but there are many tests that should be
performed regularly. This paper describes
these tests, and how often they should be
performed in order for the user to be confident
that their autoclave is functioning properly and
within the requirements of the regulatory
Introduction Figure 1
Diagram of a horizontal steam autoclave
There are four general types of sterilizers
namely, Gamma Irradiation, Gas Sterilization, An alternative method is used in vertical
Dry Heat and Moist Heat. Whilst validation of autoclaves. See figure 2. Water is placed in
all types of sterilizers follows the same basic the bottom of the chamber and heated by an
principles, by far the most prevalent type in electrical element. The resulting steam drives
South Africa are steam or moist heat the air out of an evacuation port near the top of
autoclaves and this paper therefore deals the chamber. Again the evacuation port is
specifically with this type. closed once all the air has been removed and
the steam pressure is allowed to build.
Method of Operation
Steam autoclaves generally follow the
principles shown in Figure 1. Water is heated
and the steam pressure is built up in the jacket. valve
Once sufficient pressure is obtained, the steam
is allowed to enter the chamber, thereby driving
the air out of the drain port. Once all the air
has been replaced by steam, the drain valve
closes and steam pressure builds up in the Steam
chamber. The resultant pressure causes the
temperature in the chamber to rise to the
required point, usually 121 or 135 °C.
Some type of autoclaves have a vacuum Element
function that pumps out the air before the
steam is allow to enter. This method is much
faster and more efficient. Figure 2 Diagram of vertical autoclave
Generally an autoclave cycle consists of 3 Load Types
stages viz. heating, sterilizing, de-pressure.
Vertical autoclaves may have a “water fill” Autoclaves are used to sterilize several
stage before the heating stage. Autoclaves different types of loads:
fitted with vacuum facility may have vacuum
stages before the heating stage and also as Solid – metal, glass, plastic
part of the depressurizing stage.
Porous – linen, gowns, paper, gauze,
complex instruments, hollow tubes
Liquid – water, saline, media
Laboratory waste – Petri dishes,
sample bottles, syringes 
There are various methods of validation,
Heating Sterilizing Depressure Complete depending on the usage of the autoclave.
Figure 3 Typical autoclave cycle The instrumentation fitted to an autoclave will
vary depending on the complexity and price of
Why Validate? the autoclave. A vertical autoclave may only
be fitted with a pressure gauge (also marked
in ° C) and a pressure regulator. A more
complex, fully automated large autoclave may
have a computer controlled display showing
various temperature and pressures throughout
the workings of the autoclave. Typically though,
jacket pressure and chamber pressure would
be indicated, along with chamber temperature.
Validation requires that these instruments be
checked for accuracy.
Most autoclaves are electrically powered and
all steam autoclaves require some form of a
water supply to produce steam. The electrical
supply must be able to handle the maximum
peak power of the autoclave. The quality of the
water supply will affect the quality of the steam
The drainage system must be able to handle
Figure 4 Temperature and Physical Control of the maximum flow of water and condensate
and should be able to tolerate 100 ° 
As can be seen from Figure 4, if the
temperature in an autoclave does not reach
121 ° not all spores will be destroyed in the
typical cycle time of 20 minutes. Validation is
therefore required to ensure that the autoclave
is operating correctly and that complete
sterilization is being achieved.
Validation that both water quality and steam
quality comply with the sterilizer
Validation is described as a documented specification
procedure for obtaining, recording and
interpreting data required to show that a the chamber is capable of withstanding
process will consistently comply with its specified maximum pressure. This
predetermined specifications.  test may be a legal requirement and
should be performed by a suitably
In the case of autoclaves the validation process certified organisation.
may be broken down into the following tests:
Installation Checks The performance qualification (PQ) tests
Installation Tests actually check that the autoclave is not only
Commissioning Tests functioning correctly, but also that sterilization
Performance Qualification is taking place. Analysis of documented PQ
Thermometric Tests results can also assist with pro-active
Microbiological Tests  maintenance schedules.
According to EN554:1994 “Sterilization of A thermometric test to determine the
medical devices – Validation and routine temperature profile inside the chamber
control of sterilization by moist heat” , the throughout the holding time, using a data
Commissioning tests need only be performed logging system and multiple probes placed
at initial installation and after certain repairs throughout the chamber volume.
while the Performance Qualification tests Simultaneous monitoring of the chamber
should be performed regularly and routinely. pressure is also useful in checking the
efficiency of the air removal/replacement
“Commissioning: Obtaining and documenting Once qualification of the empty chamber has
evidence that equipment has been provided been accepted, load testing should be
and installed in accordance with its performed. Here, similar probes as used in
specification and that it functions within pre- monitoring the temperature profile, are placed
determined limits when operated in accordance inside typical loads and the heat transfer time is
with operational instructions”  determined during the sterilization cycle.
These tests should be repeated for each type
Commissioning tests should include checking: of load and/or preprogrammed cycle that for
which it is intended to use the autoclave.
that the electrical supply is suitable for
the autoclave During the load testing, biological indicators
may also be placed in the load to determine if
that the temperature and humidity are sterilization is in fact taking place.
sufficiently well controlled
If the autoclave is to be used to sterilize folded
that there is no interference to or from cloth, such as garments, a Bowie Dick test
other equipment should be performed to ensure complete
penetration of the steam into the cloth.
the accuracy of indicators has been
certified to national standards Maintenance intervals
the temperature and pressure of the The intervals between Performance
chamber during a sterilization cycle are Qualification tests should be determined based
within specifications on documented experience and the need, type
and previous performance of the autoclave.
the leakage into the chamber during a EA-4/10 “Accreditation in Microbiological
vacuum cycle does not exceed the Laboratories” suggests that the load
specified maximum characteristic for each cycle be determined
every two years, while the chamber
that there is no leakage of steam, water temperature and time must be monitored during
or effluent at any point during the each use. 
Regular maintenance such as gasket performance qualification tests should be fully
inspection, and cleaning of the chamber should recorded, reviewed, accepted and archived by
be performed at the manufacturers the relevant personnel in the organisation that
recommended intervals. A full service should uses the autoclave.
be performed at least annually as should the
safety check of the pressure vessel. These results may be recorded on suitable
worksheets and certificates may be issued by
Any repairs or modifications of the unit may third-party organisations that perform such
require complete, or at least partial, re- tests.
commissioning of the autoclave, including full
Performance Qualification tests.
Routine Checking Conclusion
Routine checking may be broken down into The commissioning and performance
daily, weekly, quarterly and annual checks. qualification of an autoclave and subsequent
validation of the sterilizing protocols is a costly
Daily checks should be performed by the and time consuming process, both in the actual
operator and should include the observation of procedures involved and also in the analysis
all indicators for “normal” values. and review of the resulting documentation.
On a weekly basis safety checks should be Ensuring that sterilization is occurring in the
performed such as inspection for leaks and autoclave is however of prime importance
electrical wiring faults, inspection of door seals, (otherwise why bother to autoclave in the first
correct of operation of door interlocks and high place) thus such costs should be viewed in the
temperature and low water alarms. In the case light of human safety rather than that of
of vacuum autoclaves, a vacuum leak test economics.
should also be performed.
At the same time, however, to ensure that
Quarterly checks may include verification of the qualification and validation are performed
calibration of the instrumentation, a check of correctly, the tests should only be carried out
the automatic control functions, a check of the by suitably qualified and experienced personnel
vacuum leak sensor and a thermometric test on and organisations.
a small load.
Annually, a full re-commissioning may be  A. Chandler, Introduction to Sterilization
warranted. Thermometric testing should be
performed. Load testing should be performed  European co-operation for Accreditation
as well, but different loads may be scheduled EA-04/10 Accreditation for Microbiological
into bi- or tri-annual cycles. 
Laboratories, July 2002 rev02
 European Committee for Standardization
EN 554:1994 Sterilization of medical
Documentation devices – Validation and routine control of
sterilization by moist heat, June 1994
The results of all commissioning tests and